1. Field of the Invention
The present invention relates generally to top down/bottom up coverings for architectural openings and more particularly to a system for preventing entanglement of lift cords used in such coverings for raising and lowering horizontal rails in the covering between extended and retracted positions.
2. Description of the Relevant Art
Retractable coverings for architectural openings have been in use for many years. Early forms of such retractable coverings were referred to as Venetian blinds wherein a plurality of horizontally disposed, vertically spaceable slats are supported on cord ladders and utilize a control system that allows the slats to be raised or lowered to move the covering between retracted and extended positions relative to the architectural opening in which the covering is mounted. The slats can also be tilted about horizontal longitudinal axes to move the covering between open and closed positions.
More recently, cellular shades have been developed wherein horizontally or vertically disposed cells that are transversely collapsible, extend between horizontal or vertical rails, respectively, so that by moving the rails toward or away from each other, the covering can be retracted or extended across the architectural opening.
Retractable coverings utilizing horizontal rails for extending and retracting the covering usually employ lift cord systems for raising or lowering one or more rails to effect extension or retraction of collapsible shade material that interconnects the rails. In early retractable coverings or shades, one edge of the collapsible shade material would be secured to a headrail that also included a control system for the covering while the opposite edge of the shade material was connected to a movable bottom rail which could be raised or lowered by the control system to retract or extend the covering, respectively. In other words, by lifting the lower rail toward the headrail, the shade material would collapse therebetween until the covering was fully retracted. By lowering the bottom rail, the shade material would extend across the architectural opening.
As an evolution of such retractable shades, top down/bottom up coverings have been developed, which typically include a headrail, a movable top rail and a movable bottom rail with a shade material extending between the top and bottom rails. The control system for such coverings utilize sets of lift cords which can independently raise or lower the top and bottom rail so that the covering becomes a top down covering by lowering the top rail toward the bottom rail, or a bottom up covering by raising the bottom rail toward the top rail. Further, the rails can be positioned at any elevation within the architectural opening and with any selected spacing between the top and bottom rails for variety in positioning of the shade material across the architectural opening.
The problem encountered with such retractable coverings resides in the fact that the lift cords themselves are typically wrapped around spools within the headrail and when one movable rail is moved past a position occupied by another movable rail, the lift cords sometimes become entangled on their associated spools causing malfunctioning of the covering. While efforts have been made to avoid such entanglement, efforts are still being made to deal with this problem, and the present invention has been developed as a remedy.